At present, the existence and use of powered electronic devices has become commonplace. Modern power supplies are utilized to power or charge many of these powered electronic devices. In charging applications, the power output of these power supplies may be required to be adjustable. For example, USB-PD power supplies generally have power outputs that may be adjustable and vary from approximately 3 to 21 volts (“V”). Many of these types of power supplies are off-line switching power supplies.
Conventional off-line power supplies have operational requirements that rely on bias voltages for proper operation including start-up and steady state. Specifically, conventional off-line power supplies need one or more bias-voltages to power on and function properly. Furthermore, these off-line power supplies generally include a number of circuits, components, and devices within the off-line power supply that also need individual bias-voltages to operate properly. Complicating matters, some of these circuits, components, and devices operate in a fashion where the bias-voltage of one circuit, component, or device may directly affect the bias-voltage needs of another circuit, component, or device within the off-line power supply. Moreover, in the case of an off-line power supply that generates a bias-voltage using a voltage of a winding from a switching transformer, the voltage of the winding tracks the main output of the power supply. As an example, for power supplies with an adjustable output voltage from 3-21V (7:1 Change), if a 12V bias-voltage is needed, the voltage of the winding will have a range of 12V to 84V. Unfortunately, in this example, the excess voltage of the winding will need to be dropped across a circuit to generate the bias-voltage, such as for example, using a low-dropout (“LDO”) regulator, and power will be lost (e.g., as heat). In general, the power loss will be equal to the voltage drop multiplied by the current across circuit. As such, there is a need for a system and method that creates bias-voltages for a switching power supply that has low loss.